One of the remarkable scientific discoveries of the past several decades is that the universe and Earth appear fine-tuned for life.

Philosopher of science Stephen C. Meyer explains that fine-tuning “refers to the discovery that many properties of the universe fall within extremely narrow and improbable ranges that turn out to be absolutely necessary for complex forms of life ... to exist.”

Earth’s position in the solar system is in what scientists call the Goldilocks Zone, where it’s not too hot and not too cold.

It’s important to note that the term “fine-tuning” or “fine-tuned” is a neutral description that doesn’t imply the existence of God. It’s a designation routinely used by scientists and scholars of all stripes.

Although scientific findings are always provisional, it seems difficult to avoid the conclusion that an incredibly powerful and intelligent being designed our universe to support life.

In what follows, we’ll look at the scientific credibility of fine-tuning, specific examples, possible explanations for it, and some objections to it. Fine-tuning is not surprising if Christianity is true, since God intended to create human and animal life (Genesis 1), but it is surprising in the case of naturalism, where it appears to be an astounding coincidence.

Believe the science

One will occasionally meet skeptics who believe fine-tuning is an idea invented by Christians but not taken seriously by scientists. This is a misconception, to say the least. Consider the following testimony:

• Agnostic physicist Sir Fred Hoyle: “A common sense interpretation of the facts suggests that a super intellect has monkeyed with physics, as well as with chemistry and biology, and that there are no blind forces worth speaking about in nature.”

• Atheist physicist Stephen Hawking: “The remarkable fact is that the values of these numbers seem to have been very finely adjusted to make possible the development of life.”

• Agnostic physicist Paul Davies: “The entire universe is balanced on a knife-edge, and would be total chaos if any of the natural ‘constants’ were off even slightly.” “On the face of it, the universe does look as if it has been designed by an intelligent creator expressly for the purpose of spawning sentient beings.”

• Atheist physicist Steven Weinberg: “Life as we know it would be impossible if any one of several physical quantities had slightly different values.”

It’s notable that cosmic fine-tuning was one of the reasons the distinguished atheist thinker Antony Flew changed his mind about God’s existence, as recounted in his 2007 book “There Is a God: How the World’s Most Notorious Atheist Changed His Mind.”

Against all odds?

Philosopher Robin Collins points out, “If the initial explosion of the big bang had differed in strength by as little as one part in 10⁶⁰ [i.e., 1 followed by 60 zeros], the universe would have either quickly collapsed back on itself, or expanded too rapidly for stars to form. In either case, life would be impossible.”

This is a mind-boggling number. Collins likens this improbability to “firing a bullet at a one-inch target on the other side of the observable universe, twenty billion light years away, and hitting the target.”

He also observes that “if gravity had been stronger or weaker by one part in 10⁴⁰, then life-sustaining stars like the sun could not exist.”

If gravity were slightly stronger, stars would burn out in millions, rather than billions, of years (our sun is about 4.6 billion years old). If gravity were slightly weaker, most stars would never form at all — or would be too small and cold.

Oxford mathematician and philosopher John Lennox helps us understand this vast improbability as follows:

Cover America with coins in a column reaching to the moon (380,000 km or 236,000 miles away), then do the same for a billion other continents of the same size. Paint one coin red and put it somewhere in one of the billion piles. Blindfold a friend and ask her to pick it out. The odds are about 1 in 10⁴⁰ that she will.

A little closer to home, Earth’s position in the solar system is in what scientists call the Goldilocks Zone, where it’s not too hot and not too cold, allowing for liquid water to exist on its surface. The size of Earth also ensures that it has the right gravity to retain an atmosphere suitable for life without being too strong to inhibit the mobility of organisms.

Many other examples could be cited, but these illustrate the almost inconceivable odds against a life-permitting universe and Earth.

By design

These numbers are so surprising that they call out for an explanation, and there seem to be only three options: physical necessity, chance, or design.

Regarding physical necessity — that the universe had to have the properties that it does — there are no good reasons to believe this. As far as scientists can tell, the universe could have had a vast range of different laws, constants, and qualities.

To cite Davies again, “There is not a shred of evidence that the [parameters of our] universe [are] logically necessary. Indeed, as a theoretical physicist I find it rather easy to imagine alternative universes that are logically consistent, and therefore equal contenders for reality.”

Regarding chance, we saw earlier how incredibly unlikely it is that any possible universe would support life. When you combine the improbabilities of all the fine-tuned parameters together, the odds against life become overwhelming. The one remaining option is design. All our experience tells us that only rational agents design things, and thus a cosmic designer is the best explanation for the universe’s fine-tuning.

Multiverse muddle

Space prohibits an extended discussion of objections to fine-tuning. I’ll briefly address two that are frequently mentioned.

The first is known as the weak anthropic principle, raised by physicist Martin Rees, among others: “Some would argue that this fine-tuning of the universe, which seems so providential, is nothing to be surprised about, since we could not exist otherwise.”

Thus, we should not be surprised that the universe is fine-tuned for life, since we are here observing that it is. But as philosopher Douglas Groothuis points out, this confuses two related but distinct ideas: 1) the truism that we couldn’t observe anything unless the universe was life-permitting and 2) an explanation of why the universe is so finely tuned. Acknowledging the first observation doesn’t negate the need to explain why, against all odds, our universe is life-permitting.

Second, some thinkers appeal to the idea of a multiverse to explain fine-tuning. If billions, or even an infinite number, of other universes exist, one of those universes will inevitably permit life. We happen to be in the lucky universe that does.

God is in the details

There is no experimental evidence, however, that a multiverse exists, and some see it as an ad hoc proposal to avoid the theistic implications of fine-tuning. As physicist John Polkinghorne writes, “Let us recognize these speculations for what they are. They are not physics, but in the strictest sense, metaphysics. There is no purely scientific reason to believe in an ensemble of universes.”

While the multiverse hypothesis is complex, ad hoc, and lacks evidence, the design hypothesis is simple (one Creator) and, as noted earlier, draws on our universal experience that only minds design things.

Thus, fine-tuning provides compelling evidence that God exists and intended to create living beings. And this sounds very much like the kind of God we find described in Genesis — one who, from the beginning, “created the heavens and the earth” and declared his creation “very good” (Genesis 1:1, 31).

A version of this essay originally appeared on the Worldview Bulletin Newsletter.